UML

Introduction to UML

1 Class diagram

classDiagram
    class MailItem {
        <<Abstract>>
        +weight: float
        +express_shipping: bool
        +destination_address: str
        +__str__(): str
        +additional_str()*: str
        +calculate_postage()*: float
    }
    class Package {
        +volume: float
        +additional_str(): str
        +calculate_postage(): float
    }
    class Letter {
        +format: str
        +additional_str(): str
        +calculate_postage(): float
    }
    MailItem <|-- Package
    MailItem <|-- Letter

2 Code

mail_item.py

from abc import ABC, abstractmethod

class MailItem(ABC):
    """Definition of a mail item
    """
    def __init__(self, weight, express_shipping, destination_address):
        """Constructor

        Parameters
        ----------
        weight : float
            Weight in grams
        express_shipping : bool
            True if the shipping mode is Express
        destination_address : str
            Destination address
        """
        self.weight = weight
        self.express_shipping = express_shipping
        self.destination_address = destination_address

    @abstractmethod
    def calculate_postage(self):
        pass

    def __str__(self):
        """Display a mail item"""
        return f"""
            Mail item :
            Destination address : {self.destination_address}
            Weight : {self.weight} grams
            Shipping mode : {self.express_shipping}
            {self.additional_str()}
            Postage price : €{self.calculate_postage()}"""

    @abstractmethod
    def additional_str(self):
        pass

letter.py

from mail_item import MailItem

class Letter(MailItem):
    """Definition of a letter"""
    def __init__(self, weight, express_shipping, destination_address, format):
        """
        Parameters
        ----------
        format : str
            Format of the letter (A3 or A4)
        """
        super().__init__(
            weight,
            express_shipping,
            destination_address
        )
        self.format = format

    def additional_str(self) -> str:
        return "Format : {}".format(self.format)

    def calculate_postage(self) -> float:
        """Calculate the postage

        Returns
        --------
        float
            Postage price
        """
        postage = 0
        if self.format == "A4":
            postage = 2.5 + self.weight * 0.001
        else:
            postage = 3.5 + self.weight * 0.001
        if self.express_shipping:
            postage *= 2
        return postage

package.py

from mail_item import MailItem

class Package(MailItem):
    """Definition of a package
    """
    def __init__(self, weight, express_shipping, destination_address, volume):
        """
        Parameters
        ----------
        volume : float
            Volume in liters
        """
        super().__init__(
            weight,
            express_shipping,
            destination_address
        )
        self.volume = volume

    def additional_str(self) -> str:
        return f"Volume : {self.volume} liters"

    def calculate_postage(self):
        """Calculate the postage

        Returns
        --------
        float
            Postage price
        """
        postage = self.volume / 4 + self.weight * 0.001
        if self.express_shipping:
            postage *= 2
        return postage

sandbox.py

from package import Package
from letter import Letter

l1 = Letter(80, False, "Bordeaux", "A4")
print(l1)

c1 = Package(3500, True, "Rennes", 2.25)
print(c1)